1. Field of the Invention
The present invention relates to an apparatus for correcting an amount of fuel injection of an internal combustion engine. More particularly, it relates to an apparatus for correcting an amount of fuel injection of an internal combustion engine which calculates whether a vapor fuel purged into an intake passage of the internal combustion engine is purged from a canister or a fuel tank, so determines an anticipated correction amount of the amount of fuel injection, and calculates a correction amount of the amount of fuel injection for correcting an air-fuel ratio of the internal combustion engine by this anticipated correction amount.
2. Description of the Related Art
Generally, the internal combustion engine is equipped with an evaporative control system which prevents a fuel vapor (hereinafter referred to as the "vapor") evaporating from a fuel storage portion such as a fuel tank, a carburetor, etc., during the stop of the internal combustion engine, from being emitted to the atmosphere. This evaporative control system lets the vapor evaporating from the fuel storage portion be adsorbed by a canister, and sucks this vapor adsorbed to the canister into the intake side by utilizing an intake negative pressure during the operation of the engine.
When processing for returning (purging) the vapor adsorbed to the canister to the intake side is carried out in such an evaporative control system, a feedback correction amount FAF of the air-fuel ratio changes in accordance with a purge gas concentration. Therefore, a regulation apparatus for regulating this feedback correction amount FAF in accordance with the purge amount must be provided to the evaporative control system.
An example of such a regulation apparatus is described in KOKAI (Japanese Unexamined Patent Publication) No. 62-131962, for example. This prior art apparatus anticipates the feedback correction amount after the change on the basis of fluctuation of the feedback correction amount FAF due to the purge amount before the change when the purge amount of the vapor fuel is changed, and improves response characteristics.
However, the vapor purged into the intake passage of the internal combustion engine includes the vapor which is directly purged from the fuel tank, in addition to the vapor purged from the canister. The amount of the vapor purged from the canister changes in accordance with the adsorption amount and the emission time, while the amount of the vapor purged from the tank changes in accordance with the internal temperature of the tank and fuel properties. Accordingly, the vapor emission characteristics from the canister and the fuel tank with respect to time are not the same. For this reason, when the feedback correction amount FAF is anticipated only from the purge amount supplied from the canister to the intake passage, the anticipated value becomes incorrect, and air-fuel ratio control cannot be precisely carried out.